Please note that we produce Whole Wheat Flour (flour straight from the stones) most of time. The bolter is only run on special occassions when we have sufficient volunteers available. So we DO NOT normally have white flour available.
A video of the bolter in operation. Click on the arrow to start the video. Click on the YouTube logo to view it on YouTube (with more viewing options)
The flour from the grindstones is a mix of the entire wheat kernel which consists of bran (the outer layer), endosperm (food for the seed) and germ (the root). This is our Whole Grain flour - it contains every part of the kernel. However, it is a very heavy flour and cannot be used in all baking applications. To be able to have a finer flour (one rises more to make a lighter bread and can be used for things like cakes), the flour needs to be separated to extract the finer portion. This is done using a machine called a bolter.
The bolter contains spinning screens with various hole sizes. The flour enters one end of the bolter, the end with the finest screen. The lightest part of the flour, the fines and superfines come out from this screen. Gravity carries the remaining flour, separating out the "middlings," the "shorts," and finally, the bran. Click on the video to see the bolter in operation.
From the Bolter
A typical wheat kernel contains about 83% endosperm, 14% bran and 3% germ
Wheat to Flour
Wheat berries (middle-right, the darkest in colour - this is the kernel of the wheat prior to being ground into flour), bran
(at the back, next darkest), fine flour (white) and middlings (in-between colour).
The following are descriptions of what comes off the bolter. Of note, there are gradations between grades, the bolter is simply sorting based on the hole size in the rotating screens.
Superfine & Fine: this is the flour from our finest screen (100 mesh) and consists mostly of the endosperm of the wheat kernel. It is naturally light coloured (see photo).
Middlings & Shorts: this is the flour from our coarser screens (50 and 30 mesh) which contains the germ, coarsely ground endosperm, and some finely ground bran.
Bran: the outer layer of the wheat kernel which forms the coarsest fraction, most of the bran stays within the bolter, eventually travelling out a chute in the back end.
Our Flour Grades
The following are the grades of flour we offer for sale:
Old Stone Mill WHOLE GRAIN Flour: this is unsorted flour straight from the millstones. It contains every part of the grain. It is a heavy flour that works well for any recipe that calls for a whole grain or 100% whole wheat flour. Normally this is the only flour we have available for sale.
If we run the bolter, then we may have the following available. Please note that we normally do not have these grades available for sale:
Old Stone Mill FINE Flour: this is our fine/superfine sorting - it is naturally light (cream) coloured and will turn a bit lighter over time. It is an ideal flour for any application that requires a fine flour such as bread, pizza, cakes and pastry. In yeast applications, it will rise more than our bolted or whole grain flour.
Old Stone Mill BOLTED Flour: this is a combination of our fine flour and our middlings (about a 50:50 mix) with no bran. It has the baking characteristics of a Whole Wheat flour, but is less crunchy (no bran) than our Whole Grain flour. Recommended by Catherine Parr Traill in her mid-1800s Canadian Setter's Guide (see end of Bolter section).
Old Stone Mill BRAN: this is pure bran and can be used in any recipe that calls for bran (i.e. bran muffins).
Photo and Interpretation by Natalie Wood
The spinning screen covered cylinder inside the 14-foot (4.3 m) long bolter does the work of sorting the raw flour. The cylinder is on a slight tilt so that gravity will carry the flour from one end to the other. The mesh size of the screens are the number of holes per linear inch in those screens. The finest screen (100 mesh) is where the flour enters the bolter. This separates out the superfine and fine grade flour. The coarser segments of flour progressively drop out as they reach the coarser screens until all that is left is the bran, which drops out a chute at the end of the bolter.
Why Use the Bolter?
The main reason we (Old Stone Mill) use the bolter is that our main mission is not to make flour, it is to demonstrate the 19th century milling process. To have the visiting public be able to see and understand how flour used to be made and how critical grist mills were to early Canadian settlers. The fact that in doing this we produce a very high quality flour that we can sell in order to help fund the costs association with maintaining the Old Stone Mill, is just a bonus. But this has nothing to do with why the bolter was originally used.
These days, many of us are concerned about the nutrition value of the food we eat. Our fresh Whole Grain (unbolted) flour, produced with low heat buhr millstone grinding, is as naturally nutritious a flour as you can get. It contains every part of the grain and nutrients are not lost in the type of milling that we do.
But, step back a couple of hundred years, nutrition value was unknown, the main criteria was how well the flour worked in baking applications. A light, fluffy soft cake was preferred over a dense and crunchy cake. Same for bread. So, the bolter allowed the miller to get rid of the dense crunchy parts (the middling, shorts and bran) leaving the fine portion of the flour. This made a more saleable (commanding a higher price) product. In fact the middling, shorts and bran were often used for cattle/hog feed, not for human consumption.
The other benefit of bolting was to get rid of the wheat germ which contains fats that caused the flour to spoil (go rancid). The fine (endosperm - containing protein, no fats) portion kept fresh much longer than a flour that contained germ with its associated fats.
Today there is a demand for both the unbolted whole grain and the bolted grades of flour. Some people like having the maximum nutrition whole grain flour, but most of us today eat a varied diet which provides all those nutrients. So, our Fine flour, which is still very nutritious, is in demand because it works better in many baking applications than whole grain flour.
In Catherine Parr Traill's Canadian Settler's Guide (p.99 of the 1857 edition) she states in describing "shorts" (which would be our middlings and shorts): "This is the common name given to the inferior flour which is separated in bolting, at the mill, from the bran and fine flour, and is seldom used as a mixture in bread. This is not economical management : for mixed with fine flour, it makes sweet good bread ...". She is describing our "Bolter" grade of flour, fines mixed with middlings and shorts.